Process for selective oxidation of carbon monoxide in a hydrogen containing stream

ABSTRACT

A method of making a composition, said method comprising, spraying a substance comprising platinum and iron into or onto an alumina-containing compound is disclosed. The resulting composition can then be used in a process for oxidizing carbon monoxide with free oxygen.

FIELD OF THE INVENTION

The invention relates to the catalytic oxidation of carbon monoxide. Inanother of its aspects the invention relates to the selective oxidationof carbon monoxide in the presence of hydrogen. In yet another aspectthe invention relates to removing as much carbon monoxide as possible,preferably all carbon monoxide, from a stream containing carbon monoxideand hydrogen, particularly, to provide hydrogen feedstock for fuelcells.

BACKGROUND OF THE INVENTION

The selective oxidation of carbon monoxide in hydrogen-rich streams hasbeen of considerable technical interest for the purification of reformedhydrogen used in feed gas in ammonia synthesis. Recently, this selectiveoxidation process, sometimes referred to as preferential oxidation, hasattracted interest due to the possibility of using this technology inproviding suitable hydrogen fuel for fuel cells. Since carbon monoxideis also oxidized to provide carbon dioxide for carbon dioxide lasers,the use of a catalytic composition, which previously had been founduseful in the oxidation of carbon monoxide for use in carbon dioxidelasers, has also been investigated for adaptation for use in providingcarbon monoxide-free hydrogen for fuel cell feedstock.

A fuel cell is an electrochemical device that enables converting thechemical energy of fuels directly to electricity. A hydrogen-air polymerelectrolyte membrane (PEM) fuel cell stack is currently considered thebest means for adapting this technology to most uses. The PEM fuel cellis most efficient using gaseous hydrogen for fuel. Use of a fuelprocessor to generate a hydrogen-rich feedstock at the point of useeliminates problems of storage and distribution of the hydrogen fuel.

A fuel processor can convert fuels such as alcohol, gasoline, liquidpetroleum gas, or natural gas to a hydrogen-rich stream. By a process ofsteam reforming a stream consisting primarily of hydrogen, carbondioxide and carbon monoxide can be produced, but the product isgenerally saturated with water. Processing this stream in a shiftreactor reduces the carbon monoxide content to provide relatively morehydrogen by means of the well-known water-gas-shift reaction. Thisreaction provides a product that contains from 0.2 to 2 percent carbonmonoxide by volume, which is still sufficient to poison theplatinum-based catalytic composition at the PEM anode.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a process that is effectivefor catalytically oxidizing carbon monoxide with oxygen.

It is a further object of this invention to provide a novel method ofmaking a catalytic composition.

In accordance with the present invention, a method is provided forpreparing a composition. This method comprises, consists of, or consistsessentially of the steps of:

-   -   a) incorporating a hydrocarbon into the pores of an        alumina-containing compound such that at least half of the pore        volume of said alumina-containing compound contains said        hydrocarbon;    -   b) spraying a substance comprising platinum and iron into or        onto said alumina-containing compound to form a sprayed support;    -   c) contacting said sprayed support with a sulfide selected from        the group consisting of hydrogen sulfide and an alkyl-sulfide to        form a sulfided support;    -   d) calcining said sulfided support to form a calcined support;    -   e) contacting said calcined support with steam to form a steamed        support; and    -   f) reducing said steamed support to form said composition.

In accordance with the second embodiment, this invention a process isprovided for the selective oxidation of carbon monoxide to carbondioxide in a gaseous mixture comprising hydrogen and carbon monoxide.The process comprises, consists of, or consists essentially of:

-   -   contacting a feed stream comprising carbon monoxide, hydrogen        and oxygen with a composition prepared by the method of the        first embodiment in a contacting zone under contacting        conditions for a period to produce a product stream comprising        less carbon monoxide than the feed stream.

Other objects and advantages of the present invention will becomeapparent from consideration of the specification and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the first embodiment of this invention, a method forpreparing a composition comprises, consists of, or consists essentiallyof:

-   -   a) incorporating a hydrocarbon into the pores of an        alumina-containing compound such that at least half of the pore        volume of said alumina-containing compound contains said        hydrocarbon;    -   b) spraying a substance comprising platinum and iron into or        onto said alumina-containing compound to form a sprayed support;    -   c) contacting said sprayed support with a sulfide selected from        the group consisting of hydrogen sulfide and an alkyl-sulfide to        form a sulfided support;    -   d) calcining said sulfided support to form a calcined support;    -   e) contacting said calcined support with steam to form a steamed        support; and    -   f) reducing said steamed support to form said composition.

The preparation of the composition useful in this invention can becarried out by the following method:

The first step in this method involves incorporating a hydrocarbon intothe pores of an alumina-containing compound such that at least half ofthe pore volume of the alumina-containing compound contains thehydrocarbon.

Any suitable hydrocarbon can be used for the incorporation. Preferably,pentane is used since it can be easily vaporized. Preferably, about 50%to about 100% of the pore volume is filled with the hydrocarbon.

After the incorporating step, a substance comprising platinum and ironis then sprayed into or onto the alumina-containing compound.Preferably, the substance is comprised of chloroplatinic acid and ferricchloride.

The incorporation and the spraying steps can also be repeated to achievethe desired effect.

The resulting sprayed support is then contacted with a sulfide selectedfrom the group consisting of hydrogen sulfide and an alkyl sulfide toform a sulfided support. If an alkyl sulfide is used, preferably it isdimethyl sulfide.

The support is preferably sulfided at a temperature in the range of fromabout room temperature to about 500° C. After the sulfiding, the supportis preferably flushed with air.

The sulfided support is then calcined. Preferably, the sulfided supportis calcined at a temperature in the range of from about 150° C. to about700° C.

The calcined support is then contacted with steam to form a steamedsupport. Preferably, the calcined support is steamed by contacting itwith water saturated air at a temperature in the range of from about150° C. to about 700° C. The support can be steamed during thecalcination step described above, during the reduction step as describedbelow, or in between the calcination and reduction steps.

The reduction step can be carried out in any suitable manner, preferablyat a temperature of about 20° C. to about 650° C., more preferably atabout 200° C. to about 500° C. for about 0.5 hour to about 20 hours,preferably about 1 hour to about 5 hours to enhance the activity of thecatalyst composition for catalyzing a low temperature oxidation of COwith O₂ in the presence of hydrogen. Any reducing gas can be used:hydrogen, CO, paraffins and the like and mixture thereof. This reductionstep leaves at least a portion of the platinum of the composition in areduced valence state. The composition can also undergo treatment withsteam during the reduction step.

The composition is then recovered.

According to the second embodiment of this invention the process foroxidizing carbon monoxide in a feed stream that also contains hydrogenand oxygen comprises:

contacting a feed stream comprising carbon monoxide, hydrogen and oxygenwith a composition prepared in the first embodiment in a contacting zoneunder contacting conditions for a period to produce a product streamcomprising less carbon monoxide than the feed stream.

The feed stream to the oxidation process can be formed in any suitablemanner, such as by mixing the hydrogen that contains carbon monoxidecontaminant with the oxygen containing air at any point before or at apoint of contact with the composition.

The process for oxidizing a feed containing carbon monoxide and hydrogengas can be carried out at any temperature and pressure conditions, forany length of time, any gas hourly space velocity and any volume ratioof O₂ to CO that is suitable for selective oxidation of CO in thepresence of hydrogen. Generally, the temperature of this process is in arange of about 60° C. to about 100° C., preferably in a range of about65° C. to about 90° C., and most preferably in a range of 70° C. to 85°C.

The pressure during the oxidation process generally is in the range ofabout 10 psia to about 1000 psia, preferably 14 psia to 200 psia.

The ratio of moles of O₂ in the feed gas to the moles of CO in the feedgas will generally be in the range of about 0.5 to 8.0 mol O₂/mol CO,preferably 0.5 to 4.0 mol O₂/mol CO, most preferably 0.5 to 1.5 molO₂/mol Co.

The gas hourly space velocity (cc feed gas per cc catalyst per hour) canbe in the range of about 100 to about 200,000, preferably from about5,000 to about 50,000.

The hydrogen will generally be in the range of about 50-90 volumepercent and the inlet CO will generally be in the range of about 0.1 toabout 5 volume percent.

The following examples are presented in further illustration of theinvention and are not to be construed as limiting the scope of theinvention.

EXAMPLES Example I (Control)

A 2.90-gram quantity of chloroplatinic acid and a 3.22-gram quantity offerric chloride were dissolved in 40 mL water. Half of this solution wasthen incorporated onto 50 grams of calcined alumina and was then driedat 120° C. for 1.5 hours and calcined at 250° C. for 4 hours.

A 2-gram quantity of the composition prepared above was then charged toa ½-inch diameter stainless steel reactor and was reduced for 2 hours ata temperature of 300° C. with a hydrogen flow of 300 cc/min. After thereduction, the reactor was cooled to room temperature.

A flow of gas was then charged to the reactor. The gas comprised thefollowing: 76.3% H₂, 1.0% CO, 19.2% CO₂ and 3.5% air. The flow rate was518 cc/min, the temperature was 80° C. and the pressure was atmosphericpressure. The reaction was run for about 3 hours.

The results are shown in Table I (below).

Example II

Two grams of the composition prepared in Example I were charged to a½-inch stainless steel reactor. The composition was then reduced at 300°C. for 2 hours with hydrogen flowing through a water bubbler at 300cc/min. After the reduction, the reactor was cooled to room temperature.Then, a flow of gas was charged to the reactor that had a compositionand temperature and pressure conditions the same as in Example I. Thereaction was run for about 4 hours.

The results are shown in Table I (below).

Example III

A 2.90-gram quantity of chloroplatinic acid and a 3.22-gram quantity offerric chloride were dissolved in 40 mL of water. Half of the solutionwas incorporated onto 50 grams of calcined alumina and was then dried at120° C. for 1.5 hours. A 25-gram quantity of the composition was thencharged to a tube where it was calcined at 250° C. with both air andsteam for 4 hours.

Two grams of this calcined and steamed composition were charged to a½-inch diameter stainless steel tube reactor. The composition wasreduced at a temperature of 300° C. for two hours with a hydrogen flowof 300 cc/min. Then, a flow of gas was charged to the reactor that hadcomposition the same as in Example I and the reaction was run at theconditions disclosed in Example I. The reaction was run for about 4hours.

The results are shown in Table I (below).

TABLE I Example Description CO Conversion (%) I Control 87.2 II Steamedduring reduction 94.8 III Steamed during 92.9 calcination

The results from the first three Examples show that it can be beneficialto steam these catalyst compositions.

Example IV

A 1.06-gram quantity of chloroplatinic acid and a 0.20-gram quantity offerric chloride was added to 20 mL of acetone. This was then sprayedonto 20 grams of calcined alumina. This was dried at 120° C. over night.Then, 10 grams of the composition prepared above was steamed in air at250° C. for 4 hours.

Two grams of the composition prepared above were then placed in a ½-inchdiameter stainless steel tube reactor. The composition was reduced for 2hours with a hydrogen flow.

A flow of gas was then charged to the reactor at a rate of 530 cc/min.The gas flow comprised: 74.4% H₂, 94% CO, 18.8% CO₂, 3.4% air and 2.4%H₂O. The reaction temperature was 60° C. and the pressure wasatmospheric.

The results are shown in Table II (below).

TABLE II Example IV Composition Time on Stream (hrs) CO Conversion (%) 394.79 25 93.12 45 94.76 69 93.5 141 92.32 164 89.68

Example V

A 2.24-gram quantity of chloroplatinic acid and a 0.64-gram quantity offerric chloride were dissolved in 30 mL of acetone. This solution wassprayed onto 40 grams of calcined alumina.

A 20-gram quantity of the composition prepared above was placed in aquartz tube. A 200 cc/min. flow of nitrogen was first charged to abubbler with a quantity of dimethyl sulfide (which was set in a 27° C.water bath) and was then charged to the quartz tube. The temperature ofthe quartz tube was increased to 350° C. and remained at thattemperature for about 20 minutes. The composition was then steamed in anair flow through a water bubbler for 2.5 hours at 350° C.

Two grams of the composition prepared above was then placed in a ½-inchdiameter stainless steel tube reactor. The composition was then reducedwith a flow of hydrogen.

A flow of gas was then charged to the reactor. The gas comprised: 395cc/min H₂, 5 cc/min CO, 100 cc/min CO₂, and 18 cc/min air, and alsowater vapor. The reaction temperature was 60° C. The results are shownin Table III (below).

TABLE III Example V Composition Time on Stream (hrs) CO Conversion (%)22 97.33 46 97.08 70 95.92 142 93.74 166 92.71 186 92.28

Example VI

A solution containing 50 grams of H₂PtCl₆, 14.3 grams FeCl₃.6H₂O, and660 mL acetone was sprayed onto 892 grams of calcined alumina. A 300gram quantity of the above-prepared material was then treated withhydrogen sulfide for 15 minutes and subsequently was treated with airfor one hour. The composition was then preheated at a temperature of325° C. and was then treated with steam for 4 hours and 40 minutes.

A two gram quantity of the above-prepared composition was charged to astainless steel reactor. The composition was reduced at 300° C. for onehour with a hydrogen flow at 300 cc/min through a water bubbler.

A flow of gas was then charged to the reactor. The gas comprised: 15cc/min CO, 385 cc/min H₂, 101 cc/min CO₂ and 18 cc/min air. The reactiontemperature was 60° C. At a time of 16.5 hours on-stream, the reactionyielded a CO conversion of 91.8%.

Example VII

A solution was made, comprising 50 grams of H₂PtCl₆, 14.3 grams ofFeCl₃.6H₂O, and 500 mL of acetone. First, 300 mL of pentane was sprayedonto 892 grams of calcined alumina. Then 125 mL of the above solutionwas sprayed onto the alumina. The alumina was then dried for 20 minutes.The above three steps were repeated three times. A 50 gram quantity ofthe composition prepared above was loaded into a quartz tube and flushedwith hydrogen sulfide for ten minutes at room temperature. Thecomposition was then flushed with air for one hour at room temperature.The composition was then heated to 350° C. and steamed for 4 hours.

A 2 gram quantity of the above-prepared composition was charged to a ½inch stainless steel reactor. The composition was reduced at atemperature of 300° C. under a flow of hydrogen at a rate of 300 cc/minthrough a water bubbler for one hour. The flow of gas was then chargedto the reactor. The gas comprised 15 cc/min carbon monoxide, 385 cc/minhydrogen, 18 cc/min CO₂, and 100 cc/min air. The reaction temperaturewas 62° C. After 16 hours on-stream, the CO conversion rate was 98.0%. Asubsequent run yielded a CO conversion rate of 99.2% after 20.0 hourson-stream.

Example VIII

An 8.06 gram quantity of bis(acetylacetonate)Platinum(II) and a 10.12gram quantity of ferric acetylacetonate were added to a container andthen about 600 mL acetone is then added and the solids are dissolved.This solution is then sprayed onto 400 grams of calcined alumina. Thecomposition was dried at 150° C. for 1.5 hours and calcined at 400° C.in air for 3 hours. The composition is then placed into a 2 inchcalcination tube and was purged with nitrogen at 300° C. The compositionis then reduced in flowing hydrogen at 300° C. for 3 hours and then wascooled to room temperature while being purged with nitrogen. Thecomposition was then treated with nitric acid, dried at 150° C. for 1.5hours and calcined at 400° C. in air for three hours.

A 2 gram quantity of the composition prepared above was placed in areactor. The temperature was set at 60° C. A flow of gas was thencharged to the reactor. The gas flow comprised: 5 ml/min CO, 100 ml/minCO₂, 395 ml/min H₂, 18 ml/min air and also water vapor.

TABLE IV Example VIII Composition Time on Stream (hrs) CO Conversion (%)4 98.49 76 96.35 100 96.37 102.5 95.77 121 95.11 145 94.86 170 93.44 24191.94 266 90.68 289.5 91.78 294.5 90.11 313 90.32 315 89.2 337 89.51342.5 88.87

Example IX

A 300 ml quantity of pentane was sprayed onto calcined alumina. Then, asolution of 50 grams H₂PtCl₆.6H₂O and 14.3 grams FeCl₃ 6H₂O in 500 mlacetone is sprayed onto the alumina in a series of several applications.Between each of the acetone applications and after the finalapplication, the composition is dried by blowing air through the spheresto constant weight. Prior to each acetone application, a 300 ml quantityof pentane is sprayed onto the spheres.

The catalyst is then treated with H₂S at room temperature.

A 300 gram quantity of the catalyst was treated in a 3.5 inch tube at aflow velocity of 150 ml/min. for 15 minutes. The catalyst was thenflushed with air for one hour. A furnace was then preheated to 320° C.and a 3.5 inch tube containing 300 grams of the H₂S-treated catalyst isthen steamed by passing 1.5 L/min. of water-saturated air at 82° C.through it. The water vapor treatment is continued for 4 hours at310-320° C.

A 150 gram quantity of the steamed catalyst is added to a 2 inch tube.Water-saturated hydrogen is contacted with the catalyst at 3.5 L/min.The temperature is increased at 3° C. per minute to 270° C. and held atthis temperature for 6 hours. The temperature is then increased to 290°C. at 3° C. per minute and held for 1 hour. The heater was then turnedoff and the temperature was reduced to about 30° C. under a hydrogenflow. The catalyst was then flushed with nitrogen for ten minutes.

A 2 gram quantity of the catalyst prepared above was placed in areactor. The temperature was set at 60° C. A flow of gas was thencharged to the reactor. The gas flow comprised: 5 ml/min. CO, 100ml/min. CO₂, 395 ml/min. H₂, 18 ml/min. air and also water vapor.

TABLE V Example IX Composition Time on Stream (hrs) CO Conversion (%)2.5 99.82 94.5 99.02 122 98.75 142 98.03 170 97.72 194 97.26 267 94.66291.5 94.87 315.5 93.26 335 93.86 357.5 92.24

While this invention has been described in terms of the presentlypreferred embodiments, reasonable variations and modifications arepossible by those skilled in the art. Such variations and modificationsare within the scope of the described invention and the appended claims.

1. A method of making a composition comprising the steps of: a)incorporating a hydrocarbon into the pores of an alumina-containingcompound such that at least half of the pore volume of saidalumina-containing compound contains said hydrocarbon; b) spraying asubstance comprising platinum and iron into or onto saidalumina-containing compound to form a sprayed support; c) contactingsaid sprayed support with a sulfide selected from the group consistingof hydrogen sulfide and an alkyl-sulfide to form a sulfided support; d)calcining said sulfided support to form a calcined support; e)contacting said calcined support with steam to form a steamed support;and f) reducing said steamed support to form said composition.
 2. Amethod in accordance with claim 1 wherein said sulfide is hydrogensulfide.
 3. A method in accordance with claim 1 wherein said sulfide isan alkyl sulfide.
 4. A method in accordance with claim 3 wherein saidalkyl sulfide is dimethyl sulfide.
 5. A method in accordance with claim1 further comprising repeating step (a) and step (b).
 6. A method inaccordance with claim 1 wherein said hydrocarbon in step (a) is selectedfrom the group consisting of alkanes, alkenes and aryls.
 7. A method inaccordance with claim 1 wherein said hydrocarbon in step (a) is pentane.8. A method in accordance with claim 1 wherein said contacting of saidsulfided support with steam occurs during said calcining of step (d). 9.A method in accordance with claim 1 wherein said contacting of saidsulfided support with steam of step (e) occurs during said reducing ofstep (f).
 10. A method in accordance with claim 1 wherein said sulfidedsupport is calcined in step (d) at a temperature in the range of fromabout 150° C. to about 700° C.
 11. A method in accordance with claim 1wherein said steamed support is reduced in step (f) under reducingconditions which include a temperature in the range of from about 20° C.to about 650° C.
 12. A method in accordance with claim 1 wherein saidsteamed support is reduced in step (f) under reducing conditions whichinclude a temperature in the range of from about 200° C. to 500° C.